1. Field of the Invention
The present invention relates to methods of fabricating an exchange-coupling film, a magnetoresistive element, and a thin-film magnetic head.
2. Related Background Art
As hard disk drives have been increasing their recording density, further improvements in performances have been required in thin-film magnetic heads. As the thin-film magnetic heads, composite thin-film magnetic heads having a structure in which a magnetism detecting element such as magnetoresistive (MR) element and a magnetic recording element such as electromagnetic coil element are laminated have widely been in use. These elements reproduce data signals from a magnetic recording medium and write data signals onto the magnetic recording medium.
A magnetoresistive element provided in a thin-film magnetic head has a structure in which a nonmagnetic layer is held between a pinned magnetic layer whose direction of magnetization is fixed by an exchange-coupling magnetic field applied from an antiferromagnetic layer and a free magnetic layer whose direction of magnetization is not fixed. The direction of magnetization of the free magnetic layer changes according to the orientation of a magnetic flux emitted from a magnetic recording medium, so that the resistance value of the magnetoresistive element varies depending on the relative angle between the pinned magnetic layer and the direction of magnetization of the free magnetic layer. Therefore, when the positions of the thin-film magnetic head and magnetic recording medium are moved relative to each other while a constant current (sense current) is caused to flow through the magnetoresistive element, data signals of the magnetic recording medium can be read as voltage signals, i.e., the data signals can be reproduced by the thin-film magnetic head.
As mentioned above, the pinned magnetic layer has its direction of magnetization fixed by the exchange-coupling magnetic field applied from the antiferromagnetic layer, whereby the antiferromagnetic layer and pinned magnetic layer construct an exchange-coupling film. The direction of magnetization of the pinned magnetic layer is fixed by annealing in a magnetic field. Specifically, while applying an external magnetic field, the exchange-coupling film is heated to a temperature (blocking temperature) at which the exchange-coupling magnetic field applied from the antiferromagnetic layer to the pinned magnetic layer disappears or higher, and then is cooled. From the viewpoint of mass production, it will be more preferred if the maximum temperature during the annealing is lower. Therefore, the maximum temperature in the annealing for fixing the direction of magnetization of the pinned magnetic layer is made substantially the same as the blocking temperature in general.
Meanwhile, the strength of the exchange-coupling magnetic field determining the strength to fix the direction of magnetization of the pinned magnetic layer is an important factor for the reliability of the thin-film magnetic head. Namely, when the exchange-coupling magnetic field applied from the antiferromagnetic layer to the pinned magnetic layer is weak, the direction of magnetization of the pinned magnetic layer may tilt from its initially fixed direction during operations of the thin-film magnetic head. This may cause problems such as reduction in reproduced outputs of the thin-film magnetic head and deterioration in asymmetry of reproduced waveforms.
In conventional methods of fabricating a thin-film magnetic head, however, there have been cases where the exchange-coupling magnetic field is not strong enough to keep the thin-film magnetic head from lowering its reliability.
In view of such problems, it is an object of the present invention to provide methods of fabricating an exchange-coupling film having an exchange-coupling force greater than that conventionally available, and a reliable magnetoresistive element and thin-film magnetic head using such an exchange-coupling film.